| With the mine mining depth increas,the methane under the condition of deep reservoir exist in supercritical state,for the study of supercritical state of coal to methane adsorption characteristics,based on theoretical analysis and laboratory testing,the method of selection of shanxi datong,hebi meager-lean coal,fat coal jiaozuo Jiu Li Shan and anyang longshan anthracite four different metamorphic degree of coal as the research object,carries on the coal isothermal adsorption experiment,in combination with characteristics of pore structure of coal sample,the analysis under the supercritical state adsorption characteristics of coal to methane,the main conclusions are as follows:(1)coal sample methane depends on the adsorption quantity along with the increase of pressure are increased and first two stages,depending on the adsorption of methane at high pressure decline phenomenon can be explained from the perspective of the adsorbed phase density,in the condition of low pressure,density of the adsorbed phaseρ~A far greater than the gas phase density rho,ρ/ρ~A A approach to zero,as the pressure increases,when the density of the gas phase rho is more and more close to the density of the adsorbed phaseρ~A,1-ρ/ρ~A approach to zero,depending on the adsorption quantity and absolute adsorption quantity difference is more and more big,the difference between the apparent adsorption amount and the absolute adsorption amount continues to increase,the absolute adsorption amount will reach the maximum value with the increase of pressure,and the apparent adsorption amount must also have a maximum value,that is,after reaching the maximum value,the apparent adsorption amount will continue to decrease with the continuous increase of pressure.(2)In order to analyze the adsorption characteristics of coal to methane under supercritical condition and correctly evaluate the adsorption capacity of coal seam,it is necessary to correct the excess adsorption amount to obtain the absolute adsorption amount of coal to methane.According to the calibration results of absolute adsorption,the absolute adsorption increased with the increase of pressure.When the pressure reached about 4.59mpa,the increase of absolute adsorption slowed down and finally stabilized.The absolute adsorption amount is different from the excess adsorption amount,which refers to the actual adsorption amount of coal to methane.As the pressure increases,it is bound to reach adsorption saturation.It is shown that the absolute adsorption amount no longer increases with the increase of pressure,but eventually becomes stable with the increase of pressure.(3)based on the calculation results of methane adsorption molecular layer by coal,it is speculated that in the supercritical state,both single molecule adsorption and local two-layer adsorption exist in methane adsorption by coal.In the process of coal adsorption of methane molecules,and initial adsorption heat of condensation heat difference leads to low pressure of monolayer adsorption,with monolayer adsorption gradually become saturated,the partial single layer after high energy adsorption a methane molecules adsorption heat of gas condensation heat,will happen at this time is given priority to with gas molecules condense,coal particle surface adsorption layer adsorption effect is not obvious.(4)according to the results of thermodynamic analysis,when the temperature is constant,with the increase of pressure,the surface free energy of the four coal samples increases with the increase of pressure,which is corresponding to the increase of adsorption amount with the increase of pressure.At the same pressure,the surface free energy of the four coal samples increases with the increase of the coal sample’s metamorphism degree,which indicates that with the increase of the metamorphism degree,the adsorption of free methane on the coal surface is stronger,which shows that the coal’s adsorption of methane increases with the increase of the metamorphism degree. |
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